Code 31 (1.6L Turbo) - Turbo OVERBOOST
On turbocharged engines, exhaust gases pass from exhaust manifold through turbocharger, turning turbine blades. Compressor side of turbocharger also turns, pulling air through air filter and pushing it into intake manifold under pressure.
Wastegate is normally closed, but will open to allow by-pass of exhaust gases when an overboost condition exists. This is determined through monitored MAP sensor signals. Under normal driving conditions, ECM energizes the wastegate control (solenoid) valve. This blocks off intake manifold pressure from wastegate actuator diaphragm. When overboost condition exists, ECM will de-energize the wastegate control (solenoid) valve, allowing intake manifold pressure to act upon actuator diaphragm, opening wastegate.
As boost pressure decreases, ECM energizes wastegate control (solenoid) valve which causes wastegate to close. If MAP sensor indicates that an overboost condition exists, ECM will cut fuel delivery to prevent engine damage.
- Code 31 will set when Code 33 is not set and excessive manifold boost pressure is sensed for 2 seconds. Code 31 will be set, but CHECK ENGINE LIGHT will stay on only while overboost condition exists and for 10 seconds after manifold boost pressure has been reduced. Code 31 may be caused by White/Purple wire shorted to ground, a sticking waste-gate or actuator, control (solenoid) valve stuck in the closed position, a cut or pinched hose, an extremely dirty air filter or a faulty ECM.
- After pressure is applied to valve and then removed, actuator should slowly close wastegate. If pressure does not bleed off, vent in control (solenoid) valve could be plugged.
- With ignition on and ALDL test terminal "B" grounded, control (solenoid) valve should be energized. This closes off the manifold vacuum to the wastegate actuator.
- This checks the electrical control portion of the system. With ignition on and engine not running, solenoid should not be energized.